hy didn’t Mueller follow up on the information he uncovered himself? The regulations governing the jurisdiction of a special counsel authorize Mueller to “investigate new matters that come to light in the course of his or her investigation” with the authorization of the attorney general (or, in this case, Deputy AG Rod Rosenstein, since Jeff Sessions has recused himself). In this case, Mueller and Rosenstein apparently agreed that it was for the best not to fold an investigation into Cohen into the special counsel probe, but rather to assign it elsewhere—in this case, the U.S. attorney’s office that had jurisdiction over Cohen.
This is not to say Mueller’s team could not have legally investigated Cohen had Rosenstein authorized him to do so: the U.S. Attorney’s Manual provides protocols for how to properly investigate “an attorney who is a subject of an investigation, and who also is or may be engaged in the practice of law on behalf of clients.” By opting instead to sequester himself from the proceedings entirely, Mueller took the most restrained and conservative course of action available to him in handling the Cohen information.
According to former prosecutor Sol Wisenberg, who served as independent counsel Ken Starr’s No. 2 during the Whitewater investigation, this was not only an acceptable move for Mueller, but a wise one, both to avoid involving himself in the sordid details of the Stormy Daniels scandal and to ensure he was not opening himself to accusations of partisan misconduct.